It has been the practice in the past to test glass containers, and in particular containers which are intended to be used for pressure products, such as soft drinks and beer, by inspecting these containers for checks, both in the finish where the sealing of the container by a closure may be affected by the presence of a check and in the heel of the container which is the load and abuse bearing surface of the container. The presence of a check might result in a structural failure in the container when filled with a product under pressure. The side walls of the containers have, by and large, been inspected only by visual observation by selectors observing the containers as they move in succession past a diffuse light source. The selectors are capable of selecting out those containers which have gross defects and in some instances will be able to segregate containers having other, more obvious, defects such as checks, seeds and blisters. It has also been proposed in the past to check the structural strength of containers by subjecting them to an internal pressure test or, as is commonly known, a "bursting strength test". The "bursting strength test", however, normally is a test conducted on statistical samples of containers which are stressed by internal pressure to the point of failure and to the present time has not lent itself to being a high-speed production-type test where every container would be subjected to a specific internal pressure.
Applicants have found that by subjecting containers to a radial loading on the side wall, that those containers which have structural defects in the walls thereof or have insufficient strength to withstand a specific load, will be broken and thus effectively selected out of a line of ware being produced.